A wingtip vortex is a natural phenomenon that occurs due to pressure differences that form when a blade is subjected to fluid flow. For example, when an airfoil is provided at a positive angle, a pressure differential exists between an upper surface of the airfoil and a lower surface of the airfoil. More specifically, a pressure above the airfoil is less than atmospheric pressure, while a pressure below the airfoil equals or exceeds atmospheric pressure. Because air will flow consistent with a pressure gradient, e.g., from a high pressure region to a low pressure region, and because a path of least resistance is located at or near an airfoil's tips, air tends to flow outwardly in a spanwise manner toward a blade tip, from a bottom of the airfoil, upwardly and around the tip. In a fixed-wing aircraft, air flows outwardly from a fuselage to which a wing is mounted, toward a tip of the wing. In a rotating wing aircraft, air flows outwardly from a hub about which a propeller rotates, toward tips of the respective blades. Upon reaching the tips of the blades, the air flow spillage spirals beyond the tip of the blade and forms a whirlpool that is known as a vortex.
Wingtip vortices induce substantial amounts of drag. For example, air that spirals beyond a blade tip may combine with wash to form a rapidly spinning trailing vortex. Wingtip vortices thereby decrease the efficiency of a blade, in view of the increased energy that must be expended in order to overcome the drag induced thereby. Typically, the intensity of a wingtip vortex formed during flight is a function of a number of variables, including but not limited to the weight or speed of an aircraft, or an angle of one or more of its blades. Wingtip vortices may also create wind turbulence or other hazardous effects for other aircraft that may be operating nearby.
In the 1970s, during the midst of energy crises that drove up fuel prices around the world, researchers at the National Aeronautics & Space Administration (NASA) began experimenting with winglets, or vertical (or nearly vertical) extensions provided at the ends of wings provided on fixed-wing aircraft. NASA's research determined that the use of winglets could increase the range of fixed-wing aircraft at standard speeds, and improve the ratios of induced drag to induced lift for such aircraft by several percent, particularly where fixed winglets were provided as integral parts of the airfoils of the fixed wings.